Abstract: A series of the tests on squeal formation are carried out using a flat specimen rubbed against a ball specimen. The sound pressure level of squeal, 3-dimensional vibration accelerations of the specimen and nominal friction force are recorded during testing, which probably contain the messages on the cause to excite squeal. These signals are decomposed and analyzed using the wavelet transform technique. In the wavelet decomposing details, which correspond to the dominant frequency of the nominal friction force and inertial force, the fluctuation of the friction force is seen clearly. That demonstrates that squeal is caused by a varying friction force.

Key words: Excitation Wavelet transform, Squeal Friction-induced vibration